Why have an engine leakdown/compression test?
This is a reliable way of measuring engine wear & likely indicator of the life left in an engine.
Compression Test
This is a test of the engines ability to compress the air-fuel mixture.
Leakdown Test
This is similar to a compression test in that it tells you how well your engine's cylinders are sealing. Instead of measuring pressure, it measures pressure loss.
Both tests are very useful for problem diagnosis.